A RE can be found in European populations, mainly on the first and less frequently on the second and third mandibular molar6, with a frequency varying from 0.7% to 4.2%2,7-13 (Tab. 1). On the other hand, in population with Mongoloid characteristics, such us Chinese, Eskimo and American Indians, a RE occurs with a frequency varying from 5% to more than 50%3,5,8,12,14-33 (Tab. 2). Because of its high frequency in these populations, the RE is considered as a normal morphological variant. Curzon5 suggested that certain traits, such as the 3-rooted molar, had a high degree of genetic penetrance, as its dominance was reflected in the fact that pure Eskimo and Eskimo/
Caucasian mixes had similar prevalence of the trait. In a recent study34, the radiological examination of 4050 children in a Korean population revealed a positive correlation between the presence of an additional root in primary and permanent molars. When an additional root was present in a primary molar, the probability of the posterior adjacent molar to have an additional root, too, was greater than 94.3%34. This result indicates the existence of a significant prognostic factor for the correct diagnosis of a RE. A RP can be found mainly on the third mandibular molars, and less frequently on the second and first mandibular molars, with a frequency varying from 0.5% – 1%6. This macrostructure is very rare and occurs less
frequently than the RE.